Non-pneumatic tire

ABSTRACT

This non-pneumatic tire is provided with a tread ring, a wheel which is arranged radially inside of the tread ring, and spokes which are interposed between the tread ring and the wheel. Further, the wheel has a disc part to which the vehicle shaft is linked, and a rim part which is connected on the inner peripheral side to the disc part and is joined on the outer peripheral side to the spokes. In this configuration, the average thickness (T1) of the disc part is set to be less than the average thickness (T2) of the rim part. In other words, the relation T1&lt;T2 holds.

TECHNICAL FIELD

The present invention relates to a non-pneumatic tire including a treadpart, a wheel part, and a spoke part.

BACKGROUND ART

A general tire is attached to a wheel and filled with air (hereinafterthis tire is referred to as a “pneumatic tire (air tire)”). On the otherhand, particularly a micro electric vehicle (MEV) has come to employ anon-pneumatic tire (airless tire) that can be used without being filledwith air. In this case, the non-pneumatic tire is advantageous becausedaily check of the tire pressure is unnecessary and the non-pneumatictire is free of risk of a tire puncture.

In a vehicle including non-pneumatic tires, in order to mitigate thesense of discomfort experienced by a user (driver or passenger), it isdesirable that the user can feel comfortable and steer stably in amanner similar to a vehicle including the pneumatic tires. Therefore,the non-pneumatic tire is required to exhibit the characteristicsequivalent to those of the pneumatic tire. From such a perspective,Japanese Laid-Open Patent Publication No. 2016-041573, JapaneseLaid-Open Patent Publication No. 2014-118128, and InternationalPublication No. WO 2014/188912 have made various suggestions.

SUMMARY OF INVENTION

As described in Japanese Laid-Open Patent Publication No. 2016-041573,Japanese Laid-Open Patent Publication No. 2014-118128, and InternationalPublication No. WO 2014/188912, it has conventionally been attempted toimprove the characteristics of the non-pneumatic tire by setting thestructure, the shape, and the material of a tread part or a spoke part;however, further improvement of the characteristics of the non-pneumatictire has been required.

It is a main object of the present invention to provide a non-pneumatictire exhibiting a transient characteristic similar to that of apneumatic tire at the time a vehicle makes a turn while traveling athigh speed.

A non-pneumatic tire according to one embodiment of the presentinvention includes a tread part with a cylindrical shape that is incontact with a ground surface, a wheel part disposed inside the treadpart in a radial direction, and a spoke part interposed between thetread part and the wheel part, wherein: the wheel part includes a diskpart to which an axle is connected, and a rim part whose innercircumferential side is continuously connected to the disk part andouter circumferential side is joined to the spoke part; and an averagethickness of the disk part is smaller than an average thickness of therim part.

In this case, the disk part is easily bent. Therefore, when the vehiclemakes a turn (corners), the change in responsiveness due to the speedincrease is reduced. In addition, in a high-speed range, the transientcharacteristic similar to that of a pneumatic tire can be obtained.Therefore, a sense of discomfort experienced by a user is mitigated andaccordingly, the user feels as comfortable as he feels in the vehiclehaving the pneumatic tires.

Note that it is preferable that the spoke part includes an internal ringpart to which the rim part is joined, an external ring part for whichthe tread part is provided, and a plurality of spokes that integrallyconnect the internal ring part and the external ring part. Since thespokes provide the elastic operation, external force in the travel isrelieved. In addition, it becomes easier to join the wheel part orprovide the tread part.

In the wheel part, the disk part and the rim part may be provided asseparate members and joined to each other. In this case, the shape ofthe disk part can be changed variously and the thickness and the heightof the rim part can be individually changed variously. Thus, thecollapse (or tilting) rigidity of the disk part and/or the flexuralrigidity of the rim part in the radial direction thereof can be seteasily.

The wheel part may be formed by a single member that integrally includesthe disk part and the rim part. In this case, the joining work isunnecessary. Moreover, for example, in a case of manufacturing the wheelpart from an aluminum alloy expanded material, the weight can bereduced.

According to the present invention, the average thickness of the diskpart included in the wheel part is set to be smaller than the averagethickness of the rim part that is similarly included in the wheel part.Therefore, the disk part is easily bent and the members of the wheelpart are mainly made of metal; thus, the change in spring constant dueto the increase in rotation speed hardly occurs. Accordingly, at theturning (cornering), the change in responsiveness due to the speedincrease is reduced and the transient characteristic similar to that ofthe pneumatic tire can be obtained in the high-speed range.

As a result, the sense of discomfort experienced by a user is mitigatedand accordingly, the user feels as comfortable as he feels in thevehicle having the pneumatic tires.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an overall schematic perspective view of a non-pneumatic tireaccording to one embodiment of the present invention;

FIG. 2 is an exploded perspective view of the non-pneumatic tire in FIG.1;

FIG. 3 is a side cross-sectional view of the non-pneumatic tire in FIG.1;

FIGS. 4A, 4B, and 4C are graphs each illustrating a transientcharacteristic of cornering force of various tires for each vehiclespeed;

FIG. 5 is a graph expressing a relation between load and cornering powerwhen a vehicle makes a turn while traveling;

FIG. 6 is a side cross-sectional view of a non-pneumatic tire accordingto another embodiment; and

FIG. 7 is a side cross-sectional view of a non-pneumatic tire accordingto still another embodiment.

DESCRIPTION OF EMBODIMENTS

Preferred embodiments of a non-pneumatic tire according to the presentinvention are hereinafter described in detail with reference to theattached drawings.

FIG. 1 to FIG. 3 are an overall schematic perspective view, an explodedperspective view, and a side cross-sectional view of a non-pneumatictire 10 a according to the present embodiment, respectively. Thisnon-pneumatic tire 10 a includes a cylindrical tread ring 12 (treadpart), a wheel part 14 a disposed inside the tread ring 12 in a radialdirection thereof, and a spoke part 16 a that connects the tread ring 12and the wheel part 14 a.

The tread ring 12 is formed by an annular body made of rubber with itsouter circumferential wall serving as a ground contact surface. Notethat the ground contact surface is provided with tread grooves that arenot illustrated. By the tread grooves, sufficient grip force is obtainedeven on a wet road surface.

The wheel part 14 a includes a disk part 20 a with a disk shape, and arim part 22 a with a cylindrical shape that is continuously connected tothe outside of the disk part 20 a in a radial direction thereof. In thisstructure, a hub hole 24 is formed at a center of the disk part 20 a.Through the hub hole 24, a front end part 28 of an axle 26 indicated bya virtual line in FIG. 3 is inserted. Around the hub hole 24, aplurality of bolt insertion holes 30 are formed. To each bolt insertionhole 30, a bolt part 34 provided on the axle 26 side is inserted, andthe bolt part 34 is fixed by a nut that is not illustrated.

The disk part 20 a is manufactured by, for example, press-forming ametal plate material similar to that of a conventional tire wheel, suchas a steel material, aluminum alloy, or magnesium alloy.

On the other hand, the rim part 22 a is formed by a cylindrical body,and in this case, the rim part 22 a is a member manufactured separatelyfrom the disk part 20 a. The rim part 22 a is obtained by, for example,cutting the aforementioned metal plate member as a belt-shape body,thereafter bending the belt-shape body to bring end surfaces thereofinto contact with each other, and joining the end surfaces in contact bya suitable method such as friction stir joining or welding. After theentire disk part 20 a is housed inside the rim part 22 a, an outer edgepart of the disk part 20 a and an inner circumferential wall of the rimpart 22 a are joined to each other by welding or the like, for example.

Here, when the average thickness of the disk part 20 a is T1 and theaverage thickness of the rim part 22 a is T2 (see FIG. 3), the relationof T1<T2 is satisfied. That is to say, the average thickness T1 of thedisk part 20 a is smaller than the average thickness T2 of the rim part22 a.

In this case, each of the disk part 20 a and the rim part 22 a ismanufactured by a metal plate material with substantially the samethickness. Therefore, the thickness of each of the disk part 20 a andthe rim part 22 a is substantially constant over the entire part. Thus,the relation of T1<T2 is satisfied entirely over the disk part 20 a andthe rim part 22 a.

The spoke part 16 a includes an external ring part 40 a with an annularshape to which the tread ring 12 is fitted, an internal ring part 42 awith an annular shape that is joined to the rim part 22 a, and aplurality of spokes 44 that extend radially along the diameter of thenon-pneumatic tire 10 a. An inner circumferential side of each spoke 44is integrally connected to the internal ring part 42 a, and an outercircumferential side thereof is integrally connected to the externalring part 40 a. The spoke part 16 a as described above is formed of, forexample, a polymer material such as thermoplastic resin or thermosettingresin. Preferred examples of the thermosetting resin include epoxy-basedresin, phenol-based resin, urethane-based resin, silicone-based resin,polyimide-based resin, and melamine-based resin.

The non-pneumatic tire 10 a according to the present embodiment isbasically configured as described above, and next, the operation effectthereof is described.

As described above, the disk part 20 a and the rim part 22 a in thewheel part 14 a of the non-pneumatic tire 10 a are the separate membersthat are manufactured individually. Therefore, the shape of the diskpart 20 a can be changed variously and the thickness and the height ofthe rim part 22 a can be changed variously. Thus, the collapse (ortilting) rigidity of the disk part 20 a and/or the flexural rigidity ofthe rim part 22 a in the radial direction thereof can be setparticularly easily.

The non-pneumatic tire 10 a with the above structure contributes totravelling when, for example, the non-pneumatic tire 10 a is attached tothe axle 26 of an MEV and rotated through the axle 26 by an action of amotor. In this case, the tread ring 12 is in contact with a groundsurface (road surface). In addition, the spokes 44 of the spoke part 16a and the disk part 20 a of the wheel part 14 a receive the compressivebending force that acts in a circumferential direction of thenon-pneumatic tire 10 a so as to be bent in a rotating direction. Thatis to say, the spokes 44 and the disk part 20 a function as an elasticbody.

When the MEV or the like travels, the vehicle is turned at a curve orthe like. In other words, cornering is performed. Here, a lateral forcealong a longitudinal direction of the axle 26 acts on the tread ring 12.

In a case where the slip angle of the tire has suddenly changed becauseof a sudden steering operation, a cornering force occurs with a timedelay. This phenomenon is known as a transient characteristic ofcornering, and occurs because of an influence from a change speed of theslip angle, a lateral rigidity of the tire, and a travel speed.

Each of FIG. 4A to FIG. 4C illustrates the transient characteristics ofthe cornering forces when the vehicle (MEV) including various tirestravels at 20 km/h, 40 km/h, and 80 km/h, respectively. In the drawings,a solid line expresses a slip angle input and a dashed line expressesthe transient characteristic obtained by the non-pneumatic tire 10 a. Inaddition, a one-dot chain line and a two-dot chain line respectivelyexpress the transient characteristic of the pneumatic tire, and thetransient characteristic of the non-pneumatic tire in which the averagethickness T1 of the disk part 20 a is larger than the average thicknessT2 of the rim part 22 a. FIG. 4A to FIG. 4C indicate that thenon-pneumatic tire 10 a can obtain the transient characteristic similarto that of the pneumatic tire.

Here, the average thickness T1 of the disk part 20 a is smaller than theaverage thickness T2 of the rim part 22 a. Therefore, the disk part 20 ais easily bent. Thus, a linear relation as illustrated in FIG. 5 isobtained between the load at the turning and the cornering powercorresponding to the increase rate of the cornering force. As the loadis smaller, the speed is lower, and as the load is larger, the speed ishigher.

In FIG. 5, a curved line C corresponds to the result obtained from thepneumatic tire, and a straight line M drawn with a thick solid linecorresponds to the result obtained from the non-pneumatic tiresatisfying T1>T2. Straight lines L1, L2, L3, and L4 drawn with a thinsolid line, a dashed line, a one-dot chain line, and a two-dot chainline respectively are obtained from the non-pneumatic tire 10 a and anon-pneumatic tire 10 b according to the present embodiment satisfyingT1<T2 (see FIG. 6). More specifically, the straight line L1 correspondsto a result obtained from the non-pneumatic tire 10 b including a wheelpart 14 b formed by a single member that integrally includes a disk part20 b and a rim part 22 b obtained from an aluminum alloy expandedmaterial, and T1 is 4 mm and T2 is 7 mm. The straight lines L2 to L4correspond to results obtained from the non-pneumatic tire 10 aincluding the wheel part 14 a in which the disk part 20 a and the rimpart 22 a are manufactured individually as separate parts, having T1 of2 mm, 2 mm, and 2 mm, respectively, and T2 of 2.3 mm, 2.5 mm, and 2.8mm, respectively.

In FIG. 5, it can be realized that by setting T1<T2, the change of theresponsiveness by the speed increase can be reduced although theresponsiveness is low in the low-speed range, and in the high-speedrange, the transient characteristic similar to that of the pneumatictire can be obtained. Therefore, it is possible to dispel concerns thatthe user feels a sense of discomfort. That is to say, according to thepresent embodiment, the user feels as comfortable as he feels in thevehicle having pneumatic tires.

The present invention is not limited particularly to the aforementionedembodiment and various changes can be made within the range notdeparting from the gist of the present invention.

For example, as is understood from the above description, the wheel partmay be formed by a single member that integrally includes the disk partand the rim part. The non-pneumatic tire 10 b with such a structure isillustrated in FIG. 6. Note that the same components as those in FIG. 1to FIG. 3 are denoted with the same reference signs. In addition, thereference signs 14 b, 20 b, and 22 b respectively denote the wheel part,the disk part, and the rim part.

In addition, as illustrated in FIG. 6, the thickness of the disk part 20b may be changed. In this case, the average thickness T1 may becalculated from the thicknesses of the respective portions of the diskpart 20 b (for example, T1′, T1″, and the like) and this calculatedvalue may be made smaller than the average thickness T2 of the rim part22 b.

In addition, a non-pneumatic tire 10 c illustrated in FIG. 7 may beprovided. In this case, a wheel part 14 c includes a disk part 20 c thatis flat, and a spoke part 16 c includes an internal ring part 42 cprovided with a thick part 50. Corresponding to the thick part 50, a rimpart 22 c includes an annular concave part 52.

REFERENCE SIGNS LIST

-   -   10 a to 10 c: non-pneumatic tire    -   12: tread ring    -   14 a to 14 c: wheel part    -   16 a, 16 c: spoke part    -   20 a to 20 c: disk part    -   22 a to 22 c: rim part    -   26: axle    -   30: bolt insertion hole    -   40 a: external ring part    -   42 a, 42 c: internal ring part    -   44: spoke    -   50: thick part

What is claim is:
 1. A non-pneumatic tire comprising a tread part with acylindrical shape that is in contact with a ground surface, a wheel partdisposed inside the tread part in a radial direction, and a spoke partinterposed between the tread part and the wheel part, wherein: the wheelpart includes a disk part to which an axle is connected, and a rim partwhose inner circumferential side is continuously connected to the diskpart and outer circumferential side is joined to the spoke part; and anaverage thickness of the disk part is smaller than an average thicknessof the rim part.
 2. The non-pneumatic tire according to claim 1, whereinthe spoke part includes an internal ring part to which the rim part isjoined, an external ring part for which the tread part is provided, anda plurality of spokes that integrally connect the internal ring part andthe external ring part.
 3. The non-pneumatic tire according to claim 1,wherein in the wheel part, the disk part and the rim part are providedas separate members and are joined to each other.
 4. The non-pneumatictire according to claim 1, wherein the wheel part is formed by a singlemember that integrally includes the disk part and the rim part.